1. Field of the Invention
The present invention relates to heat transfer and more particularly concerns methods and apparatus for rapidly and efficiently removing heat from a heat source.
2. Description of Related Art
Various types of optical image projection systems, such as liquid crystal video projectors, for example, require a light source of very high intensity in order to project a relatively small image of an image source, such as a cathode ray tube, for example, at a distance upon a larger screen with sufficient illumination intensity for viewing in ambient light. The requisite high intensity of light is commonly provided by an arc lamp, such as a xenon arc lamp, which generates a very high intensity of light not only in the visible region, but also in the infrared region. The video projection system, of course, being a light viewing device, can usefully employ light energy only in visible wavelengths, between about 400 and 700 nanometers, for example. However, light energy in near infrared wavelengths, roughly between about 780 to 2500 nanometers, not only is not useful since it is not perceptible to the human eye, but tends to heat the various parts of a projector to such a degree as to significantly degrade or even destroy operability. The commonly used xenon arc lamp provides a significant amount of energy in the near infrared spectrum. Therefore, to avoid degradation or destruction of sensitive parts, including the liquid crystal light valve itself for example, the heat of this arc lamp must be dissipated.
Heat dissipation presently employed in systems of this nature generally are heat sinks that are formed of solid blocks or of solid blocks with an arrangement of heat dissipating fins formed of thermally conductive material. However, the speed and efficiency at which such heat sinks absorb and dissipate heat is poor. A number of problems result from the use of heat dissipating heat sinks in optical systems. The heat sink itself is subject to melting when it is unable to dissipate heat at a rate sufficient to handle all of the incident energy. A dichroic mirror, often termed a "cold" mirror, is frequently employed to filter out infrared energy by reflecting visible light to the projection system and passing infrared light to the heat sink. However, the heat energy passed through the mirror can result in reflection or black body radiation from the thermal mass of the heat sink which may be re-radiated back to and possibly through the cold mirror, and thus back into the heat sensitive optical system components. This can cause cracks or other structural weaknesses in the cold mirror. The re-radiated heat can degrade the coating on the cold mirror, which may cause the coating to flake off. As the coating degrades, light in the visible spectrum will pass through the mirror, together with the light in the near infrared region, thereby degrading efficiency of the optical portion of the system.
Still further, because of the relatively slow dissipation time of the thermal mass of a heat sink, the time it takes for the heat sink and other optical components in a system to cool down after system shut off can be relatively long, sometimes in the order of a quarter of an hour. Another problem due to relatively slow heat dissipation is an excessively high electrical power consumption of the overall system. High power consumption results from the use of high capacity fans and other cooling devices that are required to prevent excessive build-up of heat. Optical systems employing standard heat sinks tend to be large, because when excessive heat buildup is likely, system components must be separated from one another by adequate margins so that cool air can circulate to supplement heat dissipation.
A still further negative effect of the standard heat sink on the infrared filtering devices and on system electrical power consumption is the decrease in overall system lifetime and reliability.
Accordingly, it is an object of the present invention to provide for heat transfer by methods and apparatus that eliminate or minimize above mentioned problems.